Anthropometry is the science of measuring the shape of the spine and the effect of loads on the spine. One of the results of such measurements is a positive diagnosis of scoliosis and lordosis. These are conditions resulting from displacement from the normal of the spinal vertabrae. Lordosis is defined as the anteriorposterior malposition of the spinal processes whereas scoliosis is the lateral malposition thereof.
Live body anatomical measurements, particularly relative spinal position measurements fall into three categories, in vivo measurements; radiological measurements and surface mapping relative to anatomical reference points.
Three-dimensional computer-aided x-ray analysis of the human spine was reported by Shu in 1974 (J.Biomech 7,161-169). Variations were developed by Kraty in 1975 (Photogrammatica 31: 195-210) and Brown et al in 1976 (J.Biomech 9: 355-365).
Kraty located and recorded the transverse and spinous processes of each vertabra in both frontal and lateral projections and built up projection from triangles formed by connecting the transverse and spinous processes. These were extended by further connection to form polygons. This technique presented problems in patient movement during repeated repositioning of the x-ray machine.
Brown et al recorded bi-planar x-rays with a reference frame provided by radio-opaque indices embedded in Plexiglass panels located between the x-ray sources and the film. Each vertabra was thus modeled as a tetrahedron whose four vertices were the two pedicles and the superior and inferior vertabral body centers. The location data on each vertabra was digitized and the determination of the extent of curvature was made and compared with a manual determination on lateral x-ray. The angles compared favorably within 5 degrees. Projections were also plotted for visual assessment.
A study of the configuration of the spine in response to static loading was reported by Tichaner et al (J.Am Industr. Hyg Assn 34: 4(1973)) and named Lordisometry. This employed a two dimensional measuring device which consisted of two aluminum rods each hinged to an upright support. The angular displacement of each rod was measured by a sine-cosine potentimeter mounted at each hinge.
The potentimeter outputs, after electronic enhancement, were converted to X and Y coordinates of each point measured and plotted on an X-Y recorder. The reference points selected were the tip of the sacrum, L3, T8, C7, C3 and the midpoint of the superior nuchal line. From the coordinates of these points, the cervico-occipital, thoracocervical, lumbothoracic, lumbosacral and sacral angles relative to the horizontal were calculated and assessed.
A tracer for mapping anatomical surfaces for the study of carpal tunnel syndrome was developed by Armstrong et al (J.Biomech 12: 397(1979)). This mapper consisted of two orthogonally mounted linear potentimeters which rotated freely about a linear differential voltage transformer. Encoded points in space were scaled and represented as spherical coordinates. These coordinates were then converted to Cartesian coordinates, stored on a diskette and plotted. This device permitted the representation of the flexor digitorum profundus tendon (of the second digit) in flexed, intermediate and extended positions.
Gold et al as reported by Tichauer had demonstrated (17th Conference American Assoc. for Automotive Medicine at Oklahoma City OK Nov. 73) a three-axis kinesiometer which provided displacement, velocity and acceleration signatures of hand guided objects in space.
The apparatus consisted of three coplanar linear potentiometers located at the vertices of a right triangle mounted perpendicular to the task board. A pulley was mounted on the shaft of each potentiometer in conjunction with a spring-activated take up wheel. This provided constant tension in the string that was wrapped around each pulley. All three of the strings were connected to a ring which was fitted to a finger of the active hand being measured. This permitted a point by point determination of the instantaneous displacement, along with its first and second derivatives. The device was sufficiently sensitive to reproduce dangerous motion patterns and tremors.
Recently thermography has been used, Cooke et al (Clin. Orthop. 148: 172-176, 1980)), to detect minor scoliotic curvatures based on the asymmetry in spinal infra-red emission due to slightly asymmetric blood flow in scoliotic individuals. While theoretically viable, problems of calibration temperature control, equipment cost etc. militate against this method.
Moire topology has also been investigated for non-radiographic scoliosis screening by Wilner (Orthop.Scand. 50: 295 (1979)). The basic technique consists of producing interference patterns from a 1000 watt point source on the back of a subject standing in front of a vertical wire screen consisting of strands of 1 mm black nylon wire spaced 1 mm apart.
The interference of the light projected through the screen produces contour lines (shadows) at given distances from the screen on the subject's back. The contours are analagous to a topographical map with each contour proportional to the elevation of the back relative to the screen. Though slight asymmetries are detectable, fringe difference as related to Cobb angle, yield a rather large scatter. For this reason assessment of curvature progression over time with this technique is doubtful. However this method would be very useful in school screening programs. Such programs have been demonstrated as potentially effective.
Though radiography is capable of thoroughly documenting spinal geometry, the hazards associated with x-ray exposure are well-known.
Thermography and Moire topology may be of value in screening programs for scoliosis. However, neither of these techniques is able to quantify, at present, lateral displacement nor have measurements been taken to relate such displacement to underlying anatomical reference points for adequate mapping to determine subsequent progression or recession (and cure).